Effect of Global Regulatory Factor DasR on Spiramycin Production in Streptomyces ambofaciens

Spiramycin is a macrolide antibiotic derived from the industrial strain Streptomyces ambofaciens, and its biosynthesis is regulated by transcriptional regulators (TRs). DasR, as a TR belonging to the GntR family, is involved in multiple cellular processes. In this study, DasR was found to exert pleiotropic regulation on spiramycin production, pigment synthesis, and morphological development of S. ambofaciens. Deletion of dasR promoted spiramycin production and delayed sporulation, and the dasR deletion strain ΔdasR exhibited a 33.5% increase in spiramycin production compared to the wild-type strain, reaching a titer of 7675.8 mg/L, whereas overexpression of dasR enhanced pigment production. Transcriptomic analysis showed that dasR deletion significantly upregulated the expression of key genes involved in spiramycin biosynthesis, N-acetylglucosamine (GlcNAc) catabolism, acetyl coenzyme A (acetyl-CoA) synthesis, and nitrogen metabolism. In contrast, genes related to the glycolytic pathway, mycelial development, cell division, and the oxidative stress response were significantly downregulated. Furthermore, electrophoretic mobility shift assays (EMSAs) demonstrated that DasR directly bound to the key GlcNAc catabolism genes (ptsH, nagK, nagA, and nagB) and the acetyl-CoA synthase-encoding gene (acs), repressing their transcription. However, no binding signal was observed in the spiramycin biosynthetic gene cluster. These results suggest that DasR directly governs GlcNAc catabolism and acetyl-CoA biosynthesis in vitro. This study provides new insights into the genetic engineering of S. ambofaciens for enhanced spiramycin production.